The present invention relates generally to a method of cutting planar material, and more particularly to a method of providing offset compensation to a cutting blade to counter deviation and offset of the cutting path resulting from deflection forces exerted on the blade tip.
The cutting of planar material or sheet material with a cutting device is typically subject to deviations between the desired cutting path and the actual cutting path because of deflection forces exerted on the cutting tool. For example, U.S. Pat. No. 4,140,037, owned by the assignee of the present invention, provides yaw to a reciprocating cutting blade when cutting limp sheet material such as fabric in order to reduce deflection forces and thereby align the actual cutting path with the desired cutting path.
Cutting tools when cutting through rigid planar material such as natural wood or plywood are susceptible to relatively high deflection forces compared to tools cutting through limp sheet material. Cutting path precision is especially critical when cutting slots in rigid planar material such as die boards. Die boards are generally used to cut and/or crease one or more layers of sheet-type work material, such as cardboard, for use in the manufacture of various different articles. One such use, for example, is the fabrication of box and package blanks which after having been cut or creased by the die board, may be folded into finished boxes or product packages.
Usually, the die board consists of a base made from a thick piece of material such as plywood, that has a series of slots cut into it. These slots are arranged in a pattern corresponding, for example, to the outer periphery of a box or package blank, and the lines along which the blank must be folded to create the finished box or package. Rules, which generally consist of pieces of steel cut to lengths and/or bent to correspond to the slot length and configurations in the base, are then inserted into and protrude from the slots. The amount by which a particular rule extends from the slot depends on whether the rule will be employed to cut or crease the sheet material. Generally, during a cutting or creasing operation, the sheet material is positioned under the die board and pressure is applied to the board via a press, causing the rules to engage the sheet material, thereby cutting and creasing the sheet material.
In known methods of fabricating die boards, difficulties are often associated with the formation of the slots that must be cut into the die board base to accommodate the rules. Typically these slots are cut into the base in one of two ways; (1) using lasers, or (2) using a jig or band saw. The capital cost of a laser is generally very high, and the use of lasers tends to be expensive and complex. Further, a large amount of power is required to operate the laser, and the laser beam typically must be shielded using an inert gas. Another difficulty associated with using lasers is that the slots produced tend to have scalloped edges. When the rules are inserted into these slots, rather than having line contact between the slot edges and the rules, the rules engage the slot edges at discrete points corresponding to the xe2x80x9cpeaksxe2x80x9d of the scalloped edge. This reduces the stability of the rule in the die-board so as to increase the potential for inaccurate cutting and creasing when the die board is used. This problem is further exacerbated because the heat associated with the laser tends to dry out the board resulting in dimensional distortion of the slots being cut and warping of the board. A further problem also attributable to the heat of the laser is that smoke is generated from the material being cut. The smoke causes environmental problems which must be addressed, resulting in further increases in operating expense.
When a jig or band saw is employed, a starting hole must be drilled at one end of the slot to facilitate insertion of the blade associated with the saw. This requires an additional operation, thereby adding to the cost associated with fabricating the die board. Furthermore, these slots are often cut by hand with the inaccuracies resulting from human error making it difficult to insert the die board rules into the slots. The potential human error can also result in inaccurate die cutting. In addition, when using a manual process, the cut lines must be transferred by hand onto the die board.
It has been discovered that rotary cutting tools are preferable over lasers, jig saw reciprocating blades and band saw blades for cutting slots in die boards. The rotary cutting blade, which for example is in the form of a drill, makes a smooth groove and lends to accurate material removal when cutting through the die board base. Further, rotary machining is an efficient method of toolmaking and is fundamentally more precise than hand work or the burning process of a laser. As set forth in U.S. application Ser. No. 09/271,416, filed Mar. 17,1999 and owned by the assignee of the present invention, the rotary machining process employs a uniquely-shaped conical cutting tool which rotates at exceptionally high speeds to cut precise linear slots into plywood base materials. Steel rules are then inserted into these slots for cutting and creasing cartons. A drawback with employing rotary drills is that a deflection force opposing blade motion and rotation causes the tool tip to bend or deflect relative to the upper portion of the tool resulting in the deviation or offset of the actual cutting path relative to the desired cutting path. The deviation becomes more pronounced as the tool tip decreases in diameter.
In view of the foregoing, it is an object of the present invention to provide a cutting method which overcomes the above-mentioned drawbacks and disadvantages associated with deviations between the desired cutting path and the actual cutting path when performing a cutting operation on planar material.
A method of cutting planar material with a controlled cutting machine having a cutting tool includes performing a cutting test on various planar materials with the cutting machine under selected cutting conditions which produce deflection forces on the cutting tool tip due to the interaction of the blade and materials so as to cause the cutting tool tip to offset and move along deviated or offset cutting paths relative to desired cutting paths, and determining compensating offsets in order to align and coincide the actual cutting paths with the desired cutting paths. A schedule of the compensating offsets to align and coincide the actual cutting paths with the desired cutting paths is established as determined by the cutting tests. The schedule is to be repeatedly used thereafter for cutting planar material having cutting conditions associated with the schedule. Planar material is cut thereafter along desired cutting paths by advancing the cutting tool and planar material relative to one another and employing the schedule of compensating offsets to control the actual cutting paths to align and coincide with the desired cutting paths when desired cutting paths and corresponding cutting conditions arise.
An advantage of the present invention is that deviations or offsets to the cutting path because of deflection forces imposed on the cutting tool tip are reduced or eliminated without the need for the cutting apparatus to rely on complex and expensive feedback control during the cutting operation.